1. Field of the Invention
The present invention is generally related to a four cycle engine of a marine propulsion system and, more particularly, to an engine in which an exhaust manifold is cast as an integral part of the head portion of the marine engine in a way that forms a water dam, or standpipe, that prevents water from being ingested into the cylinders of the engine through the exhaust system.
2. Description of the Prior Art
Many different types of marine engines are known to those skilled in the art. More specifically, marine engines are defined herein as comprising a block portion and a head portion which, respectively, support a crankshaft and cam shafts for rotation about vertical axes. These marine engines are used in conjunction with outboard motors for attachment to a transom of a marine vessel. Marine engines can be two cycle or four cycle, with the pistons and cylinders of the engine being arranged in a V-configuration, opposed piston movement, or an in-line configuration.
Marine engines are provided with an exhaust system in which the exhaust gases from all of the cylinders are typically collected within an exhaust manifold and then conducted to an exhaust outlet of the outboard motor, either under or above the surface of the body of water in which the related marine vessel is operated.
One problem that occurs in marine engines is referred to as water ingestion. This occurs, under certain circumstances, when water is disadvantageously drawn in a reverse direction through the exhaust system and into one or more cylinders of the engine through their exhaust ports. Water ingestion can cause serious problems and severe damage when it occurs. Water ingestion can occur during rapid deceleration modes of operation, particularly when the engine is mounted on the marine vessel at a position low enough to place one or more of the cylinders near or below the level of the body of water in which the marine vessel is operated.
Another concern with regard to marine engines is the cost of manufacturing and assembling the engine and its related components. The exhaust manifold of a marine engine is typically cast as a separate part and then attached to the engine. When a separate exhaust manifold component is attached to an engine, the mating surfaces must be sealed and the components must be rigidly bolted together. The use of a separate exhaust manifold increases the cost of manufacturing a marine engine. In an outboard application, it is typical for the exhaust manifold to be cast as an integral part of the cylinder block of the engine, with a separate cover component used to seal the water jacket.
Another concern related to marine engines is the dissipation of heat generated by the combustion events within the combustion chambers of the engine. Hot exhaust gases must be expelled from the engine in an efficient and expeditious manner and the heat associated with the exhaust gases typically raise the temperature of associated components to relatively high temperatures. Known marine engines place the exhaust manifold on or within the block portion of the engine. Since the combustion chambers of the engine are located within the head portion, the existence of the exhaust manifold on or within the block portion of the engine creates two regions of extreme heat generating processes. The combustion events occur within the combustion chambers and therefore generate significant heat within the head portion of the engine. The passage of the hot exhaust gases through a manifold on or within an engine block creates excessive heat in the manifold itself and associated components within the block portion of the engine. As a result of these two sources of heat within the engine, the engine's cooling system must accommodate the removal of heat from these two heat loads which are not necessarily proximate each other.
U.S. Pat. No. 4,965,997, which issued to Suzuki et al on Oct. 30, 1990, describes an exhaust system for an outboard motor. The exhaust gas systems are intended to prevent the ingestion of water into the cylinders of an alternate firing multiple chamber internal combustion engine. The exhaust passages are provided with a restricted communication with each other at a point that is above the water under all running conditions so as to prevent water ingestion. In one embodiment, the exhaust passages communicate with an above the water exhaust gas discharge independently of each other and the restricted communication is provided between the passages by a restricted opening in an exhaust pipe. In another embodiment, the exhaust pipe forms an expansion chamber and the individual exhaust passages communicate with this expansion chamber at points close to each other through restricted openings for providing the communication.
U.S. Pat. No. 4,787,869, which issued to Shiozawa on Nov. 29, 1988, describes a water lock device for a marine propulsion system. Several embodiments of marine propulsion exhaust systems include water lock devices for precluding the entry of water into the engine through its exhaust ports. In each embodiment, the water lock device comprises a control valve that has flow openings for permitting the flow of exhaust gases through the control valve even when the control valve is in its closed position. The flow openings are, however, positioned so as to prevent the flow of water into the engine under these conditions. The openings also create different effective areas so that exhaust pressure tends to open the valve and water pressure tends to close the valve.
U.S. Pat. No. 5,970,926, which issued to Tsunoda et al on Oct. 26, 1999, describes an engine cooling system for an outboard motor. It includes first exhaust passages formed in a cylinder head, a second exhaust passage formed in a cylinder block and communicating with the first exhaust passages, and a cooling water passage having water jacket portions formed around the combustion chambers. The cooling water passage includes a first water jacket and a second water jacket. The cylinder head and the cylinder block are fixedly connected together by bolts. The second exhaust passage opens at a joining surface of the cylinder block along cylinders, which opening is surrounded by the bolts. The cooling water passage has water jacket portions formed between the bolts in the joining surface of the cylinder block such that they surround the opening of the block exhaust passage.
U.S. Pat. No. 6,055,970, which issued to Takahashi on May 2, 2000, describes a control system for an outboard motor. The control system includes a feedback control which obtains feedback data from a combustion condition sensor. The motor includes an engine positioned in a cowling having a vertically extending output shaft in driving relation with a water propulsion device of the motor. The engine has at least one combustion chamber and an air/fuel charging system for delivering air and fuel into the combustion chamber for combustion therein. The motor includes an exhaust system for routing exhaust from the engine to a point external to the motor. The exhaust system includes exhaust passage leading from the chamber to a main exhaust passage which extends vertically downward to an exhaust guide positioned below the engine. A passage leads from the exhaust guide into an expansion chamber and thereon to an exhaust discharge. The feedback control is arranged to adjust the ratio of air and fuel supplied to the combustion chamber and includes a combustion condition sensor mounted to exhaust gas flowing through that portion of the exhaust system positioned above the exhaust guide.
U.S. Pat. No. 4,684,351, which issued to Watanabe et al on Aug. 4, 1987, describes an outboard engine structure. The structure includes an extension case having a hollow portion formed therein and extending downwardly, the extension case being coupled with a lower surface of a crankcase of the vertical type engine, and including a driving shaft contained in the hollow portion of the extension case for transmitting power from the crankshaft of the engine to a propeller shaft. A cylinder block is connected at the rear of the engine with a cylinder head and slidably receives a piston on its cylinder bore, an exhaust passage block is interposed between the cylinder head and an extension section projecting rearwardly at the top of the extension case, and an exhaust port in the cylinder head communicating through an exhaust passage formed in the block with the hollow portion of the extension case. A water jacket is provided to surround the combustion chamber in the cylinder and extends axially of the cylinder bore to an intermediate portion thereof, and the inlet and outlet passages for the water jacket are formed in the cylinder head.
U.S. Pat. No. 4,346,676, which issued to Tyner on Aug. 31, 1982, discloses a two-cycle v-engine with an integrally cast exhaust manifold. The exhaust manifold for a water cooled, two-cycle, V-6 crankcase compression, outboard motor engine is cast integrally with the engine cylinder block.
The patents described above are hereby expressly incorporated by reference in the description of the present invention. These patents also illustrate the basic structures of various types of outboard motors. Therefore, the basic components of an outboard motor that are not directly related to the present invention will not be further described herein.
In view of the prior art, it would be significantly beneficial if a marine engine could be provided in which the number of components are reduced in order to decrease the cost of manufacture and assembly. It would further be a significant benefit if a marine engine could be provided in which the exhaust system was constructed in a way that inhibited the reverse flow of water through the exhaust system to the cylinders of the engine from the body of water in which a marine vessel is operated.